If there is no "able bodied" men (physical or spiritual) , sisters could do the job. Here in Europe, a last few years sisters serve at conventions as monitors, contribution-box guards, literature distributors, responsible for info-desk, welcoming visitors at entrance, etc., mostly young and pretty sisters. No one complains :)
About head covering, if I remember correctly, it is mandatory only if female serve as "teacher", not for doing technical jobs.